Flexible curtains for concertina-type doors already exist. Generally speaking, a door of this type comprises a flexible curtain made of reinforced plastic material, with the curtain being stiffened at regular intervals by reinforcing bars. The side edges of the curtain are guided during up and down movement by being received in vertically extending grooves as provided, for example, by channel section door posts. The reinforcing bars generally have wheels at their ends, thereby facilitating curtain folding and curtain deployment. The door is operated by a motor which drives a shaft having the top ends of door-raising straps fixed thereto. The bottom ends of the straps are fixed to the bottom reinforcing bar of the curtains, and some of the intermediate reinforcing bars are fitted with strap-guiding means, such as loops through which the straps pass freely.
These are two reasons why the above-described door is not draft-proof. Firstly, when the reinforcing bars have wheels at their ends, the wheels hold the side edges of the flexible curtain at a distance from the bottoms of the curtain-receiving grooves, thereby leaving gaps along the entire height of the side edges of the door, thereby allowing heat to be exchanged between the inside and the outside. Secondly, the side edges of the flexible curtain are not held tightly between the side walls of the grooves, since sufficient space must be left between the side walls of the grooves to receive the folds of the curtain when the door is fully open. This spacing is thus large relative to the thickness of the curtain when the curtain is fully deployed and the door is closed. In the closed position, the vertical side edges of the door are free to move backwards and forwards across the gap between the side walls of the grooves. Gusts of wind and other changes in pressure between the inside and the outside thus cause the door to flap back and forth.
Various solutions have already been proposed to improve the draft-proofing round the vertical edges of concertina-type doors. For example, proposals have been made to partially close the open slots of the side grooves by means of inwardly directed lips constituted by brushes having bristles that lie in horizontal planes and that extend obliquely relative to the side walls of the grooves. FIGS. 1, 2, and 3 are diagrammatic horizontal sections through three channel-section door posts 1 showing three implementations of such draft-proofing lips. FIG. 1 shows a post 1 having a single brush 2 extending inwardly from its outside flange. FIG. 2 shows a similar arrangement except that the brush 3 extends outwardly from the inside flange of the post. Finally, FIG. 3 shows a post having both an outside brush 2' and an inside brush 3'. The brushes have flexible bristles and provide good draft-proofing when pressed firmly against the flexible curtain. Unfortunately, the brushes are rarely pressed in a continuous manner against the curtain. Thus, good draft-proofing is only obtained when there is enough excess outside pressure (usually wind) to press the door against the inside brushes 3 or 3' (FIG. 2 or 3), or when there is sufficient excess inside pressure to press the door against the outside brushes 2 or 2' (FIG. 1 or 3). When brushes are provided on both sides (the FIG. 3 configuration) it is still not possible to fit brushes which are long enough to ensure that one or other of the brushes is always pressed against the curtain, since that does not leave enough room for the curtain to fold concertina-like when the door is opened.
Another solution (described in French patent number 83 10970) consists in fitting one of the sides of each of the door-receiving grooves with a corresponding movable draft-proofing device which is automatically pressed against the corresponding side edge of the flexible curtain when the door is fully closed, thereby pressing the curtain against the other sides of the grooves, which other sides may advantageously be fitted with brushes similar to those described above. This provides draft-proofing. However, the equipment required is complex, and thus expensive.
A problem common to the brush-only solutions described with reference to FIGS. 1 to 3 is that since the brushes are fixed (regardless of which one of the sides of the grooves they are fitted to), they have to co-operate with a moving curtain. This considerably reduces their efficiency.
Preferred embodiments of the present invention avoid the above-mentioned drawbacks.